Field of the Invention
The present invention is in the area of rotary kilns, such as, for example, are used in the manufacture of cement.
Rotary kilns can be particularly large-scale installations, often with a kiln or furnace length greater than 50 m.
Different fuels can be used for heating the kiln.
Related Art
In general, a rotary kiln has at least one main burner for primary fuel, such as oil, gas and pulverised coal. Options for adding other fuels, so-called secondary fuels, can be provided. As secondary fuels, many materials come into consideration, including plastic waste, textile waste, old tyres and the like. These secondary fuels are generally supplied by compressed air as small particles, shreds or scraps. Typically, a secondary fuel has a lower calorific value than the primary fuel. As a consequence, its complete combustion often requires additional measures, in particular, to prevent or reduce the emission of pollutants.
The basic construction of a rotary kiln is, for example, described in EP 0 866 295 A1. It proposes to improve combustion by using an oxygen lance to supply liquid oxygen.
Likewise, the basic construction of a rotary kiln is, for example, described in EP 1 065 461 B1. Improving the combustion of secondary fuel with the addition of oxygen is also proposed there.
In U.S. Pat. No. 6,318,278 B1, a rotary kiln is described as it may be constructed in the present invention. This document also shows the use of an oxygen lance in a rear internal combustion area, whereby also a supply of oxygen held at an angle to the direction of the main burner is taken into consideration.
EP 0 726 437 A1 is concerned with different oxygen lances in a rotary kiln, whereby one of the oxygen lances is introduced into the centre of a burner assembly. However, the use of a secondary fuel is not covered here.